Currently, the back light systems of the liquid crystal displays (LCDs) including large-scale LCD TVs and middle-scale LCDs for notebooks mainly utilize cold cathode fluorescent lamps for providing necessary light thereof. As the scale of the LCD TV increases, there are design principles therefor further proposed, wherein hot cathode fluorescent lamps with high watt quantity and low operation voltage are provided for back light of the LCD TV.
No matter they are cold or hot cathode fluorescent lamps, the operations for both the lamps are characterized for high impedance before being lightened up, wherein an extremely high voltage is necessary therefor. After the lamps are lightened up, the impedance of the lamps thereof would decrease, and the voltage drop for keeping the lamps light is rather lower than that for lighting up. Compared with the traditional electromagnetic transformer for the power module of the back light, the piezoelectric transformer bears such advantages as high efficiency in transformation, low emitting heat, small and low profiled, high safety, and convenience in manufacture thereof. Besides, the piezoelectric transformer is inherently characterized in having different step-ups for different impedance of loads in accordance with the characteristics of the cold/hot cathode fluorescent lamps, wherein the piezoelectric transformer affords to provide an extremely high voltage applied to the cold/hot cathode fluorescent lamps when they are in a high-impedance state before being lightened up, and further provides an appropriate operation voltage for the lamps when the step-ups for the piezoelectric transformer decrease as the impedance of the lamps decreases after they are lightened up.
However, for the power module of the back light applying the traditional electromagnetic transformer thereto, it is necessary to utilize voltage proof capacitors in series with the lamps for sharing redundant voltages. Accordingly, the piezoelectric transformer is inherently characterized in better performances for lightening up the cold and hot cathode fluorescent lamps compared with the electromagnetic transformer. Recently, there are discussions on substituting the piezoelectric transformer for the electromagnetic transformer.
As the production of the LCD TVs grows accompanying relative decrease on the price thereof, it becomes an important as to how to lower the cost for manufacturing the driving circuit for the LCD TVs, wherein it is a challenge for designing a new inverter to drive at least two cold fluorescent lamps simultaneously. In comparison with the traditional electromagnetic transformer, there is a fatal defect against lighting up in the piezoelectric transformer on the issue of driving at least two cold cathode fluorescent lamps. As abovementioned, the step-ups of the piezoelectric transformer depend on the impedance of loads, and therefore the piezoelectric transformer connected to multiple lamps might result in a decrease of the whole step-ups therein as a result of lighting up a certain lamp firstly and lead to insufficient voltage in other voltage output terminals to lighting up the other lamps, referred as a lighting issue herein. Accordingly, the present invention provides a multi-output piezoelectric transformer characterized in that the structure and the electrode configurations thereof are so designed to achieve the purpose of reducing the effects of the variations of the impedance connected to the output terminals on the steps-up of the piezoelectric transformer and overcome the lighting issue of the multi-output piezoelectric inverter for driving lamps effectively.
The present invention provides a multi-output piezoelectric transformer utilizing the configurations of the piezoelectric resonant vibration and the output and input terminals designed to light up at least two cold cathode fluorescent lamps and lower the cost for the power module of the back light effectively to boost the competitiveness for the piezoelectric transformer in the LCD TV business.